Method and device for determining gas flow

ABSTRACT

A gas flow determination method and a corresponding gas flow determination device are described. A sensor device (SD) having a diaphragm (D) and a frame (FR) enclosing it is provided; a predetermined temperature profile is created on the diaphragm (D);  
     the gas flow to be determined is directed over the diaphragm (D) in a predetermined direction of flow (F); the change in the temperature profile caused by the gas flow is detected; and  
     the gas flow is determined on the basis of the change thus detected. In particular, the temperature at a third location on the diaphragm (D) upstream from the first location and optionally at a fourth location downstream from the second location is regulated at a value corresponding to the local value of the predetermined temperature profile. In this way, the effect of soiling on the diaphragm (D) may be minimized effectively.

BACKGROUND INFORMATION

[0001] The present invention relates to a gas flow determination method having the steps: providing a sensor device having a diaphragm and a frame enclosing it; creating a predetermined temperature profile on the diaphragm; directing the gas flow to be determined over the diaphragm in a predetermined direction of flow; measuring the change in the temperature profile caused by the gas flow; and determining the gas flow on the basis of the change thus detected. The present invention also relates to a corresponding gas flow determination device.

[0002] Although applicable to any desired gas flows, the present invention and the problems on which it is based are explained here with respect to an air flow meter on board a motor vehicle.

[0003]FIG. 2 shows a cross section through a known gas flow determination device in the form of such an air flow meter.

[0004] This air flow meter has a sensor device SD having a diaphragm D and a frame FR enclosing it. Sensor device SD is manufactured in one piece with diaphragm D and frame FR enclosing it by silicon micromechanical technology. C denotes a mount in the form of a carrier plate.

[0005] In addition, a temperature profile generating device is provided to create a predetermined temperature profile on diaphragm D.

[0006] A heating device is used for heating a central region H of diaphragm D to a predetermined temperature to create a trapezoidal temperature profile on diaphragm D which has a plateau in the central region dropping essentially linearly toward the edge region.

[0007] Curve A of the standardized temperature profile shown above that indicates the status of the temperature profile without oncoming flow. Curve B indicates the status of the temperature profile with oncoming flow. The oncoming flow with air thus yields a change in the temperature profile on diaphragm D in the region which drops essentially linearly toward the edge region without oncoming flow. This change originates from the heat transport of the oncoming gas in direction of flow F.

[0008] A detection device T1, T2 composed of two temperature sensors in the form of Pt resistors is designed so that it detects the change in temperature dT1 caused by the gas flow at a first location on diaphragm D upstream from heated central region H and the change in temperature dT2 caused by the gas flow at a second location on diaphragm D downstream from heated central region H.

[0009] In addition, a determination device (not shown) is also provided and is designed so that it determines the gas flow on the basis of the difference between the temperature changes thus detected, this difference being given by ΔT=dT1−dT2.

[0010]FIG. 3 shows a schematic diagram of soiling on the known gas flow determination device in the form of an air flow meter.

[0011] In the case of the air flow meter illustrated in FIG. 2, there are deviations in the characteristic lines due to asymmetrical soiling S1 on diaphragm D. Due to soiling S1 shown here on the oncoming flow side, the temperature is lowered there due to the better thermal bonding at the edge of the diaphragm (lower heat resistance). In addition, there may be altered thermal coupling to the oncoming flow gas in the soiled region.

ADVANTAGES OF THE INVENTION

[0012] The gas flow determination method according to the present invention having the features of claim 1 and the corresponding gas flow determination device according to claim 6 have the advantage in comparison with the known approaches that the effect of soiling on the diaphragm may be minimized effectively.

[0013] The idea on which the present invention is based is that the temperature at a third location on the diaphragm upstream-from the first location and optionally at a fourth location downstream from the second location is regulated at a value corresponding to the local value of the predetermined temperature profile. Regulation at the third location is more important than regulation at the fourth location because greater deviations are to be expected at the third location than at the fourth location.

[0014] The subclaims contain advantageous refinements of and improvements on the respective object of the present invention.

[0015] According to a preferred refinement, the central region of the diaphragm is heated to a predetermined temperature to create a trapezoidal temperature profile on the diaphragm which has a plateau in the central region dropping essentially linearly toward the edge region.

[0016] According to another preferred refinement, the change in temperature caused by the gas flow is detected at a first location on the diaphragm upstream from the heated central region and at a second location on the diaphragm downstream from the heated central region, and the gas flow is also determined on the basis of the difference between the temperature changes thus detected.

[0017] According to another preferred refinement, a central region of the diaphragm is heated to a predetermined temperature above the temperature of the gas flow to be detected.

[0018] According to another preferred refinement, the third and fourth locations are selected so that they are located in the edge region of the diaphragm.

DRAWINGS

[0019] Exemplary embodiments of the present invention are illustrated in the drawing and explained in greater detail in the following description. They show:

[0020]FIG. 1 shows an embodiment of the gas flow determination device according to the present invention in cross section.

[0021]FIG. 2 shows a known gas flow determination device in cross section.

[0022]FIG. 3 shows a schematic diagram of soiling on the known gas flow determination device.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0023]FIG. 1 shows an embodiment of the gas flow determination device according to the present invention, likewise in the form of an air flow meter in cross section.

[0024] This air flow meter is in principle similar in design to the known air flow meter according to FIG. 2.

[0025] It also has a sensor device SD having a diaphragm D and a frame FR enclosing it, manufactured in one piece by silicon micromechanical technology, and also having a mount in the form of a carrier plate C.

[0026] The same heating device is used for heating a central region H of diaphragm D to a predetermined temperature to create a trapezoidal temperature profile on diaphragm D which has a plateau in the central region dropping essentially linearly toward the edge region.

[0027] In addition, a regulating device having two regulators R1, R2 for regulating the temperature on the diaphragm D at a value corresponding to the local value of the predetermined temperature profile is also provided at a third location upstream from the first location and at a fourth location downstream from the second location.

[0028] Curve A of the standardized temperature profile shown above that indicates the status of the temperature profile without oncoming flow. Curve B indicates the status of the temperature profile with oncoming flow. The oncoming flow with air thus yields a change in the temperature profile on diaphragm D in the region which drops essentially linearly toward the edge region without any oncoming flow. This change originates from the heat transport of the oncoming gas in direction of flow F.

[0029] Detection device T1, T2 composed of two temperature sensors is designed so that it detects the change in temperature dT1′ caused by the gas flow at the first location on diaphragm D upstream from heated central region H and the change in temperature dT2′ caused by the gas flow at the second location on diaphragm D downstream from heated central region H.

[0030] In addition, a determination device (not shown) is also provided and is designed so that it determines the gas flow on the basis of the difference between the temperature changes thus detected, this difference being given by ΔT′=dT1′−dT2′.

[0031] The effect of the soiling illustrated in FIG. 2 may be reduced in this embodiment by regulating device R1, R2 so that it no longer has any mentionable influence on the performance of the characteristic line. It therefore holds that

ΔT=dT1−dT2≈ΔT′=dT1′−dT2′

[0032] The temperature at which the system is regulated is lower than that in heated central region H but higher than that in frame FR.

[0033] If soiling S1 illustrated in FIG. 3 occurs now, for example, the resulting change in thermal conduction toward the edge of the diaphragm no longer results in a reduced temperature difference, because there is a corresponding compensation due to the increased heat output in the temperature regulating region.

[0034] Although the present invention has been described above on the basis of a preferred embodiment, it is not limited to this embodiment but instead may be modified in a variety of ways.

[0035] In particular, the present invention is not limited to an air flow meter but instead may be used for any desired gases. 

What is claimed is:
 1. A gas flow determination method comprising the steps: providing a sensor device (SD) having a diaphragm (D) and a frame (FR) enclosing it; creating a predetermined temperature profile on the diaphragm (D); directing the gas flow to be determined over the diaphragm (D) in a predetermined direction of flow (F); measuring the change in the temperature profile caused by the gas flow; and determining the gas flow on the basis of the change thus detected; characterized by the step: regulating the temperature at a third location on the diaphragm (D) upstream from the first location and optionally at a fourth location downstream from the second location to a value corresponding to the local value of the predetermined temperature profile.
 2. The method according to claim 1, characterized by the step: heating a central region (H) of the diaphragm (D) to a predetermined temperature to create a trapezoidal temperature profile on the diaphragm (D) which has a plateau in the central region dropping essentially linearly toward the edge region.
 3. The method according to claim 1 or 2, characterized by the steps: measuring the change in temperature caused by the gas flow at a first location on the diaphragm (D) upstream from the heated central region (H) and at a second location on the diaphragm downstream from the heated central region (H); and determining the gas flow on the basis of the difference between the temperature changes thus detected.
 4. The method according to claims 1, 2 or 3, wherein a central region (H) of the diaphragm (D) is heated to a predetermined temperature above the temperature of the gas flow to be detected.
 5. The method according to one of the preceding claims, wherein the third and fourth locations are selected so that they are located in the edge region of the diaphragm (D).
 6. A gas flow determination device comprising a sensor device (SD) having a diaphragm (D) and a frame (FR) enclosing it; a temperature profile generating device for creating a predetermined temperature profile on the diaphragm (D); a detection device (T1, T2) for measuring the change in the temperature profile caused by the gas flow; and a determination device for determining the gas flow on the basis of the change thus detected; characterized by a regulating device (R1, R2) for regulating the temperature at a third location on the diaphragm (D) upstream from the first location and optionally at a fourth location downstream from the second location to a value corresponding to the local value of the predetermined temperature profile.
 7. The device according to claim 6, characterized by a heating device for heating a central region (H) of the diaphragm (D) to a predetermined temperature to create a trapezoidal temperature profile on the diaphragm (D) which has a plateau in the central region that drops essentially linearly toward the edge region.
 8. The device according to claim 6 or 7, wherein the detection device (T1, T2) is designed such that it detects the change in temperature caused by the gas flow at a first location on the diaphragm (D) upstream from the heated central region (H) and at a second location on the diaphragm (D) downstream from the heated central region (H); and the determination device is designed such that it determines the gas flow on the basis of the difference between the temperature changes thus detected.
 9. The device according to one of the preceding claims, wherein the third and fourth locations are located in the edge region of the diaphragm (D).
 10. The device according to one of the preceding claims, wherein the sensor device (SD) is manufactured in one piece with the diaphragm (D) and the frame (FR) enclosing it using silicon micromechanical technology. 